Pump systems which comprise a fluid container for storing the fluid to be pumped out or the pumped in fluid are known. The fluid level fluctuates in such fluid containers. It is difficult to determine the actual throughflow or exit flow for this reason, since the delivery flow of the pump does not always correspond the throughflow.
GB 2 221 073 discloses a method which is based on time measurements on filling and emptying a fluid tank. This method has the dis-advantage that it only functions when the inflow into the fluid container is essentially constant during the pumping. As a rule, this is not the case.
EP 2 258 949 discloses a method for estimating the flow (throughflow) in a pump system with a fluid container, said method applying a routine for calibration, which is based on the assumption that the inflow into the container is essentially constant during the pumping. Thereby, an average value before switching on the pump forms a basis for the inflow. This method however is also not reliable, in particular if several pumps with several fluid containers are connected in series.